Inhibition of Lon protease by bacterial lipopolisaccharide (LPS) though inhibition of ATPase

Abstract

Lon protease, an ATP-dependent protease in Escherichia coli, degrades\rabnormal proteins and regulates several important cellular functions. Here we\rshow novel inhibitory effects of lipopolysaccharide (LPS) on Lon protease\ractivities. LPS inhibited the peptidase, protease, and ATPase activities of\rLon; and a dose-response study showed that LPS at low doses more effectively\rinhibited the ATPase activity than the peptidase one, suggesting different\rsusceptibility to LPS of these activities associated with Lon. Structure-activity relationship studies revealed that\rReLPS, detoxified LPS, and mono-phosphoryl as well as diphosphoryl\rlipid A, also showed similar inhibition, suggesting that neither O-antigen\rpolysaccharide nor O-acyl chain, but rather phosphate groups in the lipid A\rdomain, seem to have been responsible for the inhibitory effects. Besides,\rLPS was co-precipitated with Lon by an anti-Lon antibody, showing the direct\rbinding of LPS to Lon. These results suggest that LPS bound to Lon and\rinhibited the protease activity of Lon by inhibiting its ATPase activity. These\rresults also seem to be another example of a negatively charged phosphate\rgroup in membrane components of Escherichia coli being involved in the\rregulation of protease activity of Lon through binding to Lon and inhibiting\rits ATPase activity, as in the case of cardiolipin.